Study on effect of wind on natural smoke exhaust of enclosure fire with a two-layer zone model

Abstract

Effect of wind on natural smoke exhaust in enclosure fire with a two-layer zone model was studied in this paper. A “net wind pressure coefficient” was proposed to evaluate the significance of wind effect. Case calculations on quasi-steady vented stage of natural smoke exhaust were performed. It is shown that with a negative net wind pressure coefficient, performance of exhaust will be degraded by the wind, even invalidated. The critical wind speed invalidating natural smoke exhaust is found inversely proportional to the absolute value of the net wind pressure coefficient. Experimental data in a model room is presented and compared with the predicted values using the two-layer zone model. Good agreements were found between the predicted and experimental results except in the cases with a non-positive net wind pressure coefficient. Discrepancies are ascribed to the disturbance of the vent flow and stratification in the room by the wind. While activating natural smoke exhaust system in case of fire under the windy condition, positions of the smoke vent and air inlet should be located with consideration according to the wind direction to form a big positive net wind pressure coefficient as possible and to increase the exhaust efficiency.